Method of manufacturing a semiconductor device

Abstract

A silicon nitride film is first formed on a semiconductor substrate and serves as a polishing stopper film. Then, the silicon nitride film and the semiconductor substrate are etched in a predetermined region to form an isolating trench which partitions an active region. Next, a silicon dioxide film is deposited on the semiconductor substrate so that the isolating trench is filled with the silicon dioxide film. Next, first-stage chemical mechanical polishing (CMP) is performed with a SiO 2 -contained slurry which can efficiently polish the surface of the silicon dioxide film regardless of level difference. Finally, second-stage CMP is performed with a CeO 2 -contained slurry ensuring a large polishing selectivity ratio of the silicon dioxide with regard to silicon nitride films.

What is claimed is:  
     
         1 . A method of manufacturing a semiconductor device, comprising the steps of: 
 forming a silicon nitride film on a semiconductor substrate, said silicon nitride film serving as a polishing stopper film;    etching said silicon nitride film and said semiconductor substrate in a predetermined region to form an isolating trench which partitions an active region;    depositing a silicon oxide film on said semiconductor substrate so that said isolating trench is filled with said silicon oxide film;    polishing said silicon oxide film being in an exposed state to reduce level difference in a surface thereof, by employing a first slurry suitable for polishing a silicon oxide film and also suitable for reducing said level difference or making said level difference gentle; and    polishing said silicon oxide film until said silicon nitride film is exposed, by employing a second slurry which contains cerium dioxide, after said level difference in the surface of said silicon oxide film has been reduced.    
     
     
         2 . The method according to  claim 1 , further comprising a step of removing a portion of said silicon oxide film deposited on said active region by etching prior to the polishing of the same.  
     
     
         3 . The method according to  claim 1 , wherein said first slurry is a polishing agent that contains a silicon oxide.  
     
     
         4 . The method according to  claim 1 , wherein said level difference is reduced to less than 400 nm in the step of polishing employing said first slurry.  
     
     
         5 . The method according to  claim 1 , wherein the polishing of said silicon oxide film with said first slurry and the polishing of said silicon oxide film with said second slurry are executed on the same table.  
     
     
         6 . A method of manufacturing a semiconductor device, comprising the steps of: 
 forming a silicon nitride film on a semiconductor substrate, said silicon nitride film serving as a polishing stopper film;    etching said silicon nitride film and said semiconductor substrate in a predetermined region to form an isolating trench which partitions an active region;    depositing a silicon oxide film on said semiconductor substrate so that said isolating trench is filled with said silicon oxide film;    filling a surface depression in said silicon oxide film with a flattening material to reduce level difference in a surface of said silicon oxide film; and    polishing said silicon oxide film until said silicon nitride film is exposed, by employing a second slurry which contains cerium dioxide, after said level difference in the surface of said silicon oxide film has been reduced.    
     
     
         7 . The method according to  claim 6 , wherein said flattening material is formed by coating said silicon oxide film with spin-on glass.  
     
     
         8 . The method according to  claim 6 , wherein said flattening material is provided by forming a film of BPSG on said silicon oxide film and then performing a reflow process.  
     
     
         9 . A method of manufacturing a semiconductor device, comprising the steps of: 
 forming a silicon nitride film on a semiconductor substrate, said silicon nitride film serving as a polishing stopper film;    etching said silicon nitride film and said semiconductor substrate in a predetermined region to form an isolating trench which partitions an active region;    depositing a silicon oxide film on said silicon substrate so that said isolating trench is filled with said silicon oxide film;    performing wet chemical etching on a surface of said silicon oxide film to reduce level difference in the surface of said silicon oxide film; and    polishing said silicon oxide film until said silicon nitride film is exposed, by employing a second slurry which contains cerium dioxide, after said level difference in the surface of said silicon oxide film has been reduced.    
     
     
         10 . The method according to  claim 9 , wherein said wet chemical etching is executed over the entire surface of said silicon oxide film.  
     
     
         11 . The method according to  claim 9 , wherein said wet chemical etching is executed only on said active region while a non-active region is covered with a resist material.  
     
     
         12 . The method according to  claim 1 , wherein at least one of steps for filling a surface depression in said silicon oxide film with a flattening material; and performing wet chemical etching on a surface of said silicon oxide film is executed in combination with the step of the polishing which employs said first slurry.  
     
     
         13 . The method according to  claim 6 , wherein at least one of steps for polishing said silicon oxide film being in an exposed state by employing a first slurry suitable for polishing a silicon oxide film and also suitable for reducing said level difference or making said level difference gentle; and performing wet chemical etching on a surface of said silicon oxide film is executed in combination with the step of the filling which employs said flattening material.  
     
     
         14 . The method according to  claim 9 , wherein at least one of steps for polishing said silicon oxide film being in an exposed state by employing a first slurry suitable for polishing a silicon oxide film and also suitable for reducing said level difference or making said level difference gentle; and filling a surface depression in said silicon oxide film with a flattening material is executed in combination with the step of the wet chemical etching.  
     
     
         15 . The method according to  claim 2 , wherein said first slurry is a polishing agent that contains a silicon oxide.  
     
     
         16 . The method according to  claim 2 , wherein said level difference is reduced to less than 400 nm in the step of polishing employing said first slurry.  
     
     
         17 . The method according to  claim 3 , wherein said level difference is reduced to less than 400 nm in the step of polishing employing said first slurry.  
     
     
         18 . The method according to  claim 2 , wherein the polishing of said silicon oxide film with said first slurry and the polishing of said silicon oxide film with said second slurry are executed on the same table.  
     
     
         19 . The method according to  claim 3 , wherein the polishing of said silicon oxide film with said first-slurry and the polishing of said silicon oxide film with said second slurry are executed on the same table.  
     
     
         20 . The method according to  claim 4 , wherein the polishing of said silicon oxide film with said first slurry and the polishing of said silicon oxide film with said second slurry are executed on the same table.